The present invention concerns a device for evaluation electron-optical images by simultaneous observation of the electron-optical image and of a light-optical image. The invention refers in particular to the semi-automatic evaluation of images while they are produced in an electron microscope.
Devices for semi-automatic and full automatic evaluation are known for electron-optical photographs. Devices are also known for the fully automatic evaluation of images while they are produced in an electron microscope. They operate with television camera tubes and employ extensive electronic circuits or computers for the evaluation. They are therefore costly and expensive. In many cases, however, a semi-automatic device is preferable, namely when decision criteria are clearly perceptible to the eye but cannot be recognized by an automatic system. Semi-automatic devices which proceed from an object image on which an image analysis is effected are known. However, in electron microscopes, the visible image is produced on a fluorescent screen in an evacuated microscope column, and, therefore, the known semi-automatic devices require that a photographic recording first be made and processed so that such recording can be the basis on which image analysis may thereafter be effected.
For direct semi-automatic evaluation of an electron-optical fluorescent-screen image, it is advisable to observe the electron-optical image at the same time as a light-optical image. The light-optical image may include, for example, a displaceable, variable-diameter measurement diaphragm for determining particle size. A semi-transparent mirror may be arranged in front of the normal viewing window, said mirror permitting simultaneous observation of the electron-optical image and a light-optical image. The disadvantages of such a device are clear, in that brightness of the electron-optical image is greatly reduced for the observer. Furthermore, the device is expensive and takes up a large amount of space, which is inconvenient, particularly in front of the microscope column, since it limits accessibility to the operating elements of the electron microscope.